The present invention relates to a method of automatically adjusting density in a copier and other image forming devices.
In a copier and other image forming devices, it is a common practice to sense the density of an original document in order to compensate the amount of exposing light and other factors. One approach to sense document density is loading a scanner with a density sensor so that the density of a document may be sensed by the sensor prior to usual slit exposure, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 58-214144/1983. The scanner type scheme allows density to be adjusted automatically without resorting to prescanning, i.e. scanning which is effected before a document is actually scanned to form a latent image thereof. However, a problem with the density sensing system without prescanning is that due to a limitation on a sensing region the amount of information sensed is too small for image density to be optimized according to information on a document. The prescanning system, on the other hand, successfully provides density information over the entire length of a document and, therefore, promotes the ease of adjustment of image density. Nevertheless, such a system is inherently low in copying rate.
In light of the above, there has been proposed another approach which allows any desired sensing region to be selected manually in the event of image density sensing so that image density may be optimized, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 59-142573/1984. This type of scheme has a drawback that the manual operation is time- and labor-consuming. Another drawback is that because the basis for the selection of a sensing region is indefinite, the expected effect is not readily attainable when it comes to copiers which use plain papers and are used by many and unspecified persons.